The present invention relates to an electric motor control device and drive unit.
In an electric motor control that controls a drive of a three-phase electric motor by three-phase current feedback control, if gains of three-phase current sensors are unbalanced due to a variability introduced during manufacturing, variability in adjustment of a signal processing circuit, or the like, motor current pulsation or motor torque pulsation occurs. In order to prevent the problem, the current sensors are corrected (see, for example, Japanese Patent Application Publication No. JP-A-2003-259698 and Japanese Patent Application Publication No. JP-A-2005-162462), or a safety margin is provided so that the current pulsation does not cause overcurrent.
Japanese Patent Application Publication No. JP-A-2003-259698 describes a circuit through which currents of two phases of a three-phase electric motor are detected by a current sensor and multiplied by gains in multipliers. Based on those results, the remaining current of another phase is calculated to obtain the three respective phase current values, which are then used as feedback values for vector control that controls a drive of an induction motor through a pulse width modulation (PWM) inverter. The correction of the detection gains of the above-described three respective phase currents fed back to the vector control is activated when a selector switch is turned to close the correction circuit. That is, by the close of the circuit, the correction circuit converts the three respective phase currents to a d-axis value and a q-axis value by three-phase/two-phase conversion, then extracts a harmonic component contained in a d-axis current, and adjusts the gain of the multiplier of a phase so as to minimize the absolute value of the harmonic component. Then, the correction circuit finishes the correction after storing the adjusted value in a storage element, and maintains the gain of the multiplier at the adjusted value until making the correction next time.
Japanese Patent Application Publication No. JP-A-2005-162462 describes an elevator control device in which three respective phase currents of a three-phase alternating current motor for driving up and down movements of an elevator by being supplied with power from an inverter are detected by current detectors and converted to two-axis values, and error output values for making the two-axis values to be desired values are converted by two-phase/three-phase conversion and then converted to PWM signals to drive the inverter. To correct the detection gains of the respective phase currents of the electric motor, a correction command switch is switched to a correction circuit side and also a torque current command is fixed to a predetermined value, and furthermore, particular timings, such as 60 degrees, 120 degrees and the like, are determined so that the rotor electric angle of one phase is zero and the sum of the rotor electric angles of the other two phases is zero. Then, the gains of the two phases are adjusted at those timings so that the sum of the detected three-phase currents is zero.